Scheme 1.
Synthesis of compounds D1-D19. Reagents and conditions: (1) (Boc)2O, Et3N, MeOH/H2O; (2) CH3COCl, CH3OH; (3) TBTU, Et3N, THF; (4) EtOAc, HCl; (5) RSO2Cl, RCOCl, NaHCO3, THF/H2O; RNH2, triphosgene, dioxane, Et3N, DCM; (6) NH2OK, MeOH.
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